Method and apparatus for dissolving a gas into a liquid for single wet wafer processing

ABSTRACT

A method and apparatus for processing a wafer is described. According to the present invention a wafer is placed on a substrate support. A liquid is then fed through a conduit having an output opening over the wafer. A gas is dissolved in the liquid prior to the liquid reaching the output over the wafer by flowing a gas into the conduit through a venturi opening formed in the conduit. The liquid with dissolved gas is then fed through the opening and onto the wafer where it can be used to etch, clean, or rinse a wafer.

[0001] This application claims the benefit of provisional applicationserial No. 60/214,058 filed Jun. 26, 2000 entitled METHOD AND APPARATUSFOR DISSOLVING A GAS INTO A LIQUID FOR SINGLE WET WAFER PROCESSING.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to the field of semiconductorprocessing and more specifically to a method and apparatus fordissolving a gas into a liquid used for cleaning, etching, or rinsing awafer.

[0004] 2. Discussion of Related Art

[0005] Wet etching and wet cleaning of silicon wafers is usually done byimmersing the wafers into a liquid. This can also be done by spraying aliquid onto a wafer or batch of wafers. Wet wafer cleaning and etchingis traditionally done in a batch mode where several (e.g., between50-100) wafers are processed simultaneously. Because of the need a shortcycle time in chip manufacturing, there is a need for fast single waferprocessing. In wet processing the amount of dissolved gas in the liquidused for processing is very important for process results.

[0006] When performing wet etching operations, the amount of gas is veryimportant for process results. At first there are the common reactivegases such as O₂, O₃, and H₂. On the other side there are the inertgases such as N₂, Ar, and He. Both the reactive gas content and inertgas content are important in wet processing. The reactive gas can reactwith the semiconductor wafer surface or with contaminants on thesurface. The inert gases determine the amount of cavitation during amegasonic cleaning step and therefore influence the particle removal. Itis very important to control the amount of both reactive gases and inertgases dissolved into liquids when using wet processing to treatsemiconductor wafers. Sometimes it is assumed that all dissolvedreactive gases are “bad” and therefore it is assumed that theconcentration of O₂, O₃, and H₂ has to be reduced to the minimum levelpossible. However, the right amount or the absence of reactive gases isdependent on a particular process and there is not a general level ofdissolved reactive gases that is adequate for every process step.Present methods for dissolving gases into liquids include membranecontactors, bubbling chambers, spraying methods and shower type methods.A problem with these methods and apparatuses, however, is that they arebulky and expensive. They are ideal for batch processing tools but areto large and to expensive for very small single wafer tools.

[0007] Thus, there is a need for a simple and inexpensive way fordissolving the correct amount of reactive and inert gases into etching,cleaning, and rinsing liquids.

SUMMARY OF THE INVENTION

[0008] A method and apparatus for processing a wafer is described.According to the present invention a wafer is placed on a substratesupport. A liquid is then fed through a conduit having an output openingover the wafer. A gas is dissolved in the liquid prior to the liquidreaching the output over the wafer by flowing a gas into the conduitthrough a venturi opening formed in the conduit. The liquid withdissolved gas is then fed through the opening and onto the wafer whereit can be used to etch, clean, or rinse a wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1a is an illustration of a cross-sectional view of a singlewafer cleaning apparatus having a venturi for dissolving a gas into aliquid processing fluid.

[0010]FIG. 1b is an illustration showing the covering of the entiresurface area of a plate with transducers.

[0011]FIG. 1c is an illustration showing how the transducers coveredplate of FIG. 1b covers the entire surface area of a wafer beingcleaned.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0012] The present invention is a method and apparatus for dissolvinggases into a liquid in a wet processing apparatus. In the followingdescription numerous specific details are set forth in order to providea thorough understanding of the present invention. One of ordinary skillin the art will understand that these specific details are forillustrative purposes only and are not intended to limit the scope ofthe present invention. Additionally, in other instances, well-knowprocessing techniques and equipment have not been set forth inparticular detail in order to not unnecessarily obscure the presentinvention.

[0013] The present invention is a method and apparatus for dissolvingreactive and/or inert gases into a liquid and then using the liquid forwet processing. The present invention utilizes a venturi to dissolve agas or gases such as but not limited to O₂, O₃, H₂, N₂. Ar, and He intoa processing liquid supply line of a wet processing apparatus. The useof a ventui is ideally situated for dissolving gases into a liquid in asingle wafer wet processing apparatus 100 such as shown in FIG. 1a.

[0014] According to the present invention a venturi 128 is placed in aliquid supply conduit 126 before a opening such as spray or dispensingunit 114 located over a wafer support 110 which holds a wafer 108 to beprocessed as shown in FIG. 1a. In an embodiment of the present inventionthe venturi 128 is situated at or near the point of use (e.g., nearspray nozzle 114). A venturi 128 is a throat or narrowing of thecross-sectional area of supply line 126. The venturi 128 creates underpressure locally because of the increase in flow rate of the liquidflowing through venturi 128 according to the Bernouilli principle. Theuse of a Bernouilli enables gases 129 to be dissolved into the flow of aprocessing liquid even when the supply gas is at a lower pressure thanthe processing liquid supply pressure. This provides added flexibilityas to the supply of gas 129.

[0015] A gas 129 is dissolved into processing liquid through an opening127 provided in conduit 126 of venturi 128. Because of the reducedpressure of venturi 128 gas can be easily dissolved into a liquidstreaming past venturi 128.

[0016] The dissolved gas can be an inert gas such as but not limited toN₂/Ar, He, or a reactive gas such as O₃, O₂, and H₂. The gases can bedissolved in a wide variety of liquids used for wet processing such asbut not limited to etching solutions such as HF and buffered HF,cleaning solutions such as SC-1 (NH₄OH, H₂O₂, and H₂O) and SC-2 (HCl,H₂O₂, and H₂O), and rinsing solutions such DI water. For example, O₃ canbe dissolved into DI water to help rinse away chelating agents andsurfactants used in cleaning solutions. Venturi 128 is ideal fordissolving O₃ into DI water because O₃ is typically supplied at lowerpressures than the DI water is supplied into conduit 126. Additionally,inert gases such as He or N₂ can be dissolved into processing fluids inorder to provide cavitation into a liquid film 122 formed on wafer 108in order to improve the cleaning, etching, or rinsing of a wafer. Theventuri 128 of the present invention is ideal for use in a single waferprocessing apparatus such as apparatus 100 because it is a simple,quick, small, and cheap inline system for dissolving gas into a liquid.Additionally, venturi 128 can precisely control the amount of gas whichis dissolved into a liquid.

[0017] Because ventui 128 can be used to precisely control the amount ofgas dissolved into a fluid it enables a processing fluid to be generatedwhich has the appropriate gas and with the appropriate concentration atthe point of use for each process step. That is, according to anembodiment of the present invention first all gas is removed to theabsolute minimum from the processing fluid such as DI water. The removalof the gas can be accomplished at for example, the central facilitieswhere tanks 124 can be located. Once all gases have been sufficientlyremoved, a venturi 128 can be used to dissolve, at the point of use, thedesired concentration of reactive and/or inert gases into the processliquid for every process step. This will dramatically improve theuniformity of the wet process. Once the desired amount of gas isdissolved in the desired processing liquid, the liquid can be sprayed ordispensed onto wafer 108 for etching, cleaning, or rinsing the wafer.

[0018] Although venturi 128 can be used in any wet processing apparatusrequiring a dissolved gas, venturi 128 is ideal for use in a singlewafer processing apparatus, such as apparatus 100 as shown in FIG. 1a.Single wafer cleaning apparatus 100 shown in FIG. 1a includes a plate102 with a plurality of acoustic or sonic transducers 104 locatedthereon. Plate 102 is preferably made of aluminum but can be formed ofother materials such as but not limited to stainless steel and sapphire.The plate is preferably coated with a corrosion resistant fluoropolymersuch as Halar. The transducers 104 are attached to the bottom surface ofplate 102 by an epoxy 106. The transducers 104 cover the entire bottomsurface of plate 102 as shown in FIG. 1b. The transducers 100 preferablygenerate sonic waves in the frequency range between 400 kHz and 8 MHz.In an embodiment of the present invention the transducers arepiezoelectric devices. The transducers 104 create acoustic or sonicwaves in direction perpendicular to the surface of water 108.

[0019] A substrate or wafer 108 is held at distance of about 3 mm abovethe top surface of plate 102. The wafer 108 is clamped by a plurality ofclamps 110 face up to a wafer support 112 which can rotate wafer 108about at central axis. The wafer support can rotate or spin the wafer108 about a central axis at a rate between 0-6000 rpm. In apparatus 100only wafer support 112 and wafer 108 are rotated during use whereasplate 102 remains in a fixed position. Additionally, in apparatus 100wafer 108 is place face up wherein the side of the wafer with patternsor features such as transistors faces towards a nozzle 114 for sprayingcleaning chemicals thereon and the backside of the wafer faces plate102. Additionally, as shown in FIG. 1c the transducer covered plate 102has a substantially same shape as wafer 108 and covers the entiresurface area of wafer 108. Apparatus 100 can include a sealable chamber101 in which nozzle 114, wafer 108, and plate 102 are located.

[0020] During use, DI water (DI-H₂O) is fed through a feed throughchannel 116 and plate 102 and fills the gap between the backside ofwafer 108 and plate 102 to provide a water filled gap 118 through whichacoustic waves generated by transducers 104 can travel to substrate 108.In an embodiment of the present invention DI water fed between wafer 108and plate 102 is degassed so that cavitation is reduced in the DI waterfilled gap 118 where the acoustic waves are strongest thereby reducingpotential damage to wafer 108.

[0021] Additionally during use, cleaning chemicals and rinsing watersuch as DI-H₂O are fed through a nozzle 114 to generate a spray 120 ofdropless with form a thin liquid coating 122 (as little as 100 microns)on the top surface of wafer 108 while wafer 108 is spun. In the presentinvention tanks 124 containing etching, cleaning, and rinsing solutionssuch as diluted HF, de-ionized water (DI-H₂O), are coupled to conduit126 which feeds nozzle 114.

We claim:
 1. A method of processing a wafer: placing a wafer on a wafersupport; flowing a liquid through a conduit having an output openingover said support; dissolving a gas into said liquid prior to saidoutput by flowing a gas into said conduit through a venturi openingformed in said conduit; and flowing said liquid with said dissolved gasthrough said opening and onto said wafer.
 2. The method of claim 1wherein said gas is selected from the group consisting of O₃, O₂, H₂,N₂, Ar, and He.
 3. The method of claim 1 wherein said liquid comprisesHF.
 4. The method of claim 1 wherein said liquid comprises DI water. 5.The method of claim 1 wherein said liquid comprising a cleaningsolution.
 6. The method of claim 1 further comprising degassing saidliquid prior to flowing said liquid through said conduit.
 7. The methodof claim 1 wherein said gas is supplied at a lower pressure than saidliquid flowing through said conduit.
 8. The method of claim 7 whereinsaid gas is ozone (O₃).
 9. A wafer processing apparatus comprising: awafer support; a conduit for supplying a liquid to an opening positionedover said wafer support; a venturi in said conduit prior to said openingover said wafer support; and a venturi opening in said conduit at saidventuri for dissolving a gas into said liquid.
 10. The apparatus ofclaim 9 wherein said wafer support is rotatable.
 11. The apparatus ofclaim 9 wherein said wafer support is a single wafer support.